An electron beam addressed liquid crystal light valve of the cathode-ray tube (CRT) type is described in copending U.S. patent application Ser. No. 07,046,822 of Buzak et al., Liquid Crystal Light Valve With Electrically Switchable Secondary Electron Collector Electrode, filed concurrently herewith. The light valve of Buzak et al. is a form of CRT having a twisted nematic liquid crystal cell, one substrate surface of which serving as a target for a writing electron beam emitted by a writing electron gun and propagating within the tube. The target substrate comprises a thin sheet of dielectric material and forms one face of the liquid crystal cell.
The CRT also includes writing and erasing electron guns and a collector electrode positioned above and over the target surface. The erasing electron gun and the collector electrode cooperate to maintain the target surface of the cell at a desired operating electrostatic potential, which is the potential of the electrons emanating from the erasing electron gun. Polarized light propagating from an external source enters the CRT through an optically transparent entry window on one side of the tube and passes through the cell and out through an exit window. The writing and erasing guns are mounted at oblique angles relative to the target substrate to keep them out of the light path. Unwritten areas of the liquid crystal cell remain in an "OFF" state that rotates by 90 degrees the polarization direction of the light emanating from the external source. Areas addressed by the writing beam are temporarily switched into an "ON" state that leaves unchanged the polarization direction of the light emanating from the external source and thereby creates a light image pattern that is detected by an analyzing polarizer positioned in the path of light exiting the CRT exit window.
The light valve of Buzak et al. is susceptible to significant spatial variations in the luminance of the written areas across the target surface. The degree of such variations differs among different ones of light valves of the same design type. It would be desirable, therefore, to incorporate in each such light valve compensation that can be individually tailored to achieve spatially uniform light transmittance over the target surface.